1. Field of the Invention
The present invention is related to a liquid discharge recording head for performing a recording operation by discharging liquids, such as ink, from a discharge port. Specifically, it is related to an ink jet recording head for performing recording by discharging ink. The liquid discharge recording head of the present invention can be applied to devices such as a copying machine, a facsimile having a communication system, a word processor having a printing section, and a recording apparatus, which is multi-functionally combined with each device, other than a common printing device. In the present invention, “recording” also means adding an image such as a simple pattern.
2. Description of the Related Art
Japanese Patent Laid-Open No. 2002-154208 discloses a recording head mounted on an ink jet recording apparatus. Japanese Patent Laid-Open No. 2002-154208 discloses a configuration for mounting two recording element boards, having two different discharging methods, on one chip plate (supporting member) so as to achieve high-grade recording as well as high-speed recording, and at the same time, to achieve lower cost and simplifying as well as downsizing of the configuration. Such a configuration is shown in FIG. 6.
FIG. 6 is a sectional view of recording element boards 5 and 6 and support member 3 in the conventional art. FIG. 6 is equivalent to a part of the A-A′ section of the liquid discharge recording head of FIG. 8. Japanese Laid-Open No. 2002-154208 discloses that the Si boards 18 and 19, used for the two recording element boards 4 and 5, respectively, have the same thickness. A flow path forming member 20 in recording element board 4 for discharging black ink has a nozzle structure for discharging a large droplet, and for efficiently performing solid printing, by preparing the distance between the energy generating element 2 and the discharge port 11 to be longer. For the discharging method of this nozzle structure, the method of generating an air bubble in ink by driving a recording element and discharging ink by defoaming of the air bubble is adopted. On the other hand, the recording element board 5 for discharging color ink has a nozzle structure for achieving highly-accurate and high-quality recording by discharging a droplet of a small amount, compared to black ink, by shortening a distance between the energy generating element 2 and the discharge port 11, compared to black ink. For the discharge method of this nozzle structure, a method of discharging ink by having an internal pressure of an air bubble communicate with air in a negative state, the air bubble being generated in the ink by driving a recording element is adopted.
A liquid discharge recording head where two recording element boards are mounted on one support member discharges ink in a direction substantially perpendicular to a medium to be recorded in performing recording by being set in a recording apparatus as shown in FIG. 7. Also, there is some undulation on the surface of the medium to be recorded. Therefore a gap of approximately 1.2 mm is provided between the liquid discharge recording head and the medium to be recorded such that a face of the liquid discharge recording head, on which a discharge port is disposed, and the surface of the medium to be recorded do not interfere. This gap is referred to as head-to-paper distance. The most suitable distance is set for this head-to-paper distance by balancing image quality and cost.
With respect to a head disclosed in Japanese Patent Laid-Open No. 2002-154208, in the recording element board 4 for discharging black ink, the distance between the energy generating element 2 and the discharge port 11 is longer, compared to the recording element board 5, since the recording element board 4 is configured to discharge a larger droplet, compared to the recording element board 5. On the other hand, the recording element board 5 for discharging color ink has a nozzle structure where a distance between the recording element and the discharge port is shorter since the recording element board 5 is configured to discharge a smaller droplet. Thus, when the thickness of the Si substrates 18 and 19 are approximately the same, the distance between the discharge port and the medium to be recorded (head-to-paper distance) is relatively longer in the recording element board 5 for discharging color ink than in the recording element board 4 for discharging black ink. Generally, landing accuracy of discharged ink to a medium to be recorded deteriorates when the head-to-paper distance becomes longer. Therefore, droplet landing accuracy may deteriorate. The deterioration in the droplet landing accuracy of the recording element board 5 for discharging color ink is one of the reasons of color unevenness in so-called secondary color formation, formed by color inks. In the conventional product, the image quality has been improved by increasing the number of times that a recording head scans over a medium to be recorded (the number of passes). However, as demand for improved printing speed increases, the number of passes tends to decrease. At the same time, there is a demand for higher quality of images, and improvement of landing accuracy of a droplet of small amount, such as color ink, becomes more important. The smaller that the amount of the discharged liquid is, the larger the influence of the landing accuracy to a medium to be recorded and a satellite droplet, being generated accompanying a main droplet, becomes. As a result, the influence on image quality becomes more significant.
In view of the above-described problem, there is a need for improvement of image quality of a head for color ink for performing relatively small-amount discharge, without lowering image quality of a head for black ink.